Mollusca: Polyplacophora) Hiroshi Saito

Home , Acanthochitonidae, Amicula (chiton), Chitonida, Chitonina, Craspedochiton, Cryptoconchus

Bollettino Malacologico, Roma, Supplemento 5: 83-104, [2003] 2004 - Società Italiana di Malacologia

Phylogenetic significance of the radula in chitons, with special reference to the Cryptoplacoidea (Mollusca: Polyplacophora) Hiroshi Saito

Department of Zoology, National Science Museum, 3-23-1 Hyakunin-cho, Shinjuku-ku, Tokyo 169-0073, Japan, e-mail: [email protected]

ABSTRACT Polyplacophoran radular characters are reviewed and their usefulness in systematics is re-evaluated. The results suggest that radular characters are useful not only for recognition of species but also for assessment of phylogenetic relationships among species, genera or even higher taxa. In particu- lar, the petaloid process of the major lateral tooth may have taxonomic significance at family or higher levels, and the accessory process of the centro-lateral tooth is another possibly important character at higher taxonomic levels. Radular characters may be most useful in evaluation of the phylogenetic relationships within a genus and/or a family. The present study outlines the characteristics of radulae of the following cryptoplacoid genera: Craspedoplax, Craspedochiton, Notoplax, Cryptoconchus, Leptoplax, Bassethullia, Pseudotonicia, Acanthochitona, Choneplax, Cryptoplax, Hemiarthrum and Cryptochiton. Morphological comparison implies close relationships between Notoplax and Cryptoconchus and among Acanthochitona, Choneplax and Cryptoplax; paraphyly of Cryptoconchus, the presence of a number of species-groups or genera in Acanthochitona, and parallel reduction of the tegmentum within the Cryptoplacoidea.

RIASSUNTO Vengono riviste le caratteristiche della radula nei poliplacofori e ne viene rivalutato l’utilizzo in sistematica. I risultati suggeriscono che i caratteri della radula sono utili non solo per il riconoscimento delle specie, ma anche per la valutazione delle relazioni filogenetiche tra specie, generi o taxa di livello superiore. In particolare, il processo petaloide del secondo dente laterale può assumere un significato tassonomico a livello di famiglia o superiore, e il processo accessorio del primo dente laterale e’ un altro importante carattere a livelli tassonomici elevati. I caratteri della radula possono essere molto utili nella valutazione delle relazioni filogenetiche all’interno di un genere e/o di una famiglia. Il presente studio evidenzia le caratteristiche della radula dei seguenti generi criptoplacoidi: Craspedoplax, Craspedochiton, Notoplax, Cryptoconchus, Leptoplax, Bassethullia, Pseudotonicia, Acanthochitona, Choneplax, Cryptoplax, Hemiarthrum e Cryptochiton. I confronti morfologici implicano: una stretta parentela tra Notoplax e Cryptoconchus e tra Acanthochitona, Choneplax e Cryptoplax; la parafilia di Cryptoconchus; la presenza di un certo numero di gruppi di specie o generi in Acanthochitona, e un parallelismo nella riduzione del tegmentum all’interno dei Cryptoplacoidea.

KEY WORDS: Polyplacophora, Cryptoplacoidea, radula, morphology, phylogeny.

INTRODUCTION The confused and unstable state of the phylogeny of the chi- demonstrates how careful comparisons of radular characters tons led Sirenko (1997) to state that taxonomy of the class can clarify phylogenetic relationships in chitons. As a test was in a "crisis situation". He reviewed traditional charac- case, the radular morphology of the superfamily Cryptopla- ters, such as gill arrangement, egg hull morphology and coidea is described and illustrated, and its phylogenetic sig- articulamentum development, and explored some new ones. nificance is discussed. Similar attempts to establish new characters were also made, among others, by Haszprunar (1987: ultrastructure of the MATERIAL AND METHODS hypobranchial organ) and Buckland-Nicks (1995: sperm Most of the material used in this study was from museum or morphology). In order to establish more accurate phyloge- private collections and was preserved in ethanol or formalin. netic hypotheses, further useful morphological characters There were also a few dried specimens. Animal size is here should be sought to complement recent molecular studies. defined as body length (BL). I am convinced that the radula is one such character, and As the radulae of chitons have a complicated, three-dimen- that it should be re-evaluated via thorough review and sional structure, scanning electron microscopy (SEM) is extensive studies of fine morphology. Because of its structur- essential for examination of the fine morphology of each al complexity and conservative nature, the radula has not tooth. For examination by SEM, the following procedure was been fully employed in chiton taxonomy, although it is adopted: dissected radulae were boiled in KOH solution for widely used in gastropod systematics. The radula is also one to two minutes, and rinsed with tap water; they were expected to prove useful in the systematic study of then cleaned with an ultrasonic cleaner (except for some scaphopods, as pointed out by Lamprell and Healy (1998: 8: examples that were set aside for examination of the petaloid “Comparative radular morphology may yet prove a most process and accessory process), and dehydrated using a series rewarding avenue for further taxonomic research…”). Radu- of ethanol concentrations. Most of the radulae were then lar characters are also a promising tool for tackling the phy- immersed in t-butyl alcohol and dried with a JEOL JFD- logeny of chitons, but not merely on the basis of morpholog- 300 freeze dryer, while a portion were air dried (AD). All ical characters of individual species. By review of radular samples examined by SEM were observed in high vacuum characters using scanning electron microscopy, this paper mode with gold or gold-palladium coating.

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stress in the same manner as demonstrated for the gastropod radula by Solem (1972) and Hickman (1984). Some genera such as Callochiton and Notoplax have skewed radular rows. Radular teeth within the Polypla- cophora show a considerable range of morphological variability, though in many cases the radula is less variable among species in the same genus, or even between genera. Some genera in current use contain species with essentially different kinds of radulae and should be re-assessed. The occurrence of considerable ontogenetical variability (O’Neill, 1984; Sirenko, 1974, 1992) and polymorphism (Bullock, 1988b) should also be noted.

General tooth morphology Central: The central tooth shows a broad range of morphology within the class, from large to small and broad to narrow. It usually consists of a main Fig. 1. Terminology for radular teeth of chitons. plate with or without a cusp at the C, central tooth; CL, centro-lateral tooth; ML, major lateral tooth; ISL, inner small lateral tooth; OSL, outer small lateral tooth; MU, major uncinus tooth; IM, inner marginal tooth; MM, middle marginal tooth; OM, apex and a prop plate at the anterior outer marginal tooth; ps, posterior surface of the central tooth; adc, antero-dorsal corner of the centro-lateral base. The main plate is sometimes tooth; ap, accessory process; h, head; pp, petaloid process; p, pore; s, shaft. thick, and the prop plate cannot be Fig. 1. Terminologia per i denti radulari nei chitoni. C, dente centrale; CL, dente centro-laterale (o primo laterale); ML, dente laterale maggiore (o secondo laterale); separated from it. The central tooth is ISL, piccolo dente laterale interno (o terzo laterale); OSL, piccolo dente laterale esterno (o quarto laterale); MU, asymmetrical in those genera which dente laterale uncinato (o quinto laterale); IM, dente marginale interno; MM, dente marginale mediano; OM, have skewed radular rows. Usually the dente marginale esterno; ps, superficie posteriore del dente centrale; adc, angolo antero-dorsale del dente centro- laterale; ap, processo accessorio; h, testa; pp, processo petaloide; p, poro; s, parte basale. features of the central tooth are fairly consistent within species, but they The terminology of the radular teeth used in this paper basi- may vary to some extent in certain species, such as members cally follows that of Is. Taki, (1938) and Bullock (1988a) of the genus Acanthochitona. (Fig. 1). Centro-lateral: This tooth also displays a wide range of Abbreviations for names of institutions used in the text are morphology within the class. In many species it consists of as follows. two parts: a plate surrounding the central tooth, and prop FSBC: Florida Marine Research Institute; plate extending between the shafts of the adjoining centro- NSMT: National Science Museum, Tokyo; lateral teeth. In some genera, like Notoplax, the centro-lateral SAM: South Australian Museum; tooth is smaller and lower than the central tooth and lacks a USNM: National Museum of Natural History, Smithsonian cusp, while in other genera such as Ischnochiton it is taller Institution. than the central tooth and has well developed cusp. There is a minute process called the “accessory process” or Morphology of Polyplacophoran Radula “pad” near the antero-dorsal corner (Figs. 1, 2, ap). The dis- The polyplacophoran radular ribbon is cylindrical at the pos- tribution of the accessory process among chitons is unclear terior portion and flat at the anterior portion, essentially because of its minute size and deciduous nature, and it has conforming to the “cylinder model” proposed by Morris & thus not attracted much attention from past workers. So far, Hickman (1981) for the archaeogastropod radula. The work- it has been confirmed as occurring in many species in the ing movement of the chiton radula is also the same as that of Chitonina, but not for example in Radsia barnesii (Gray, the archaeogastropods (Matsukuma & Tsubaki, 1995). 1828) (Bullock, 1988b). A similar process has also been The radular teeth on the radular membrane are arranged in a found in some species of the Lepidopleurina, namely Lepto- complex three-dimensional layout. The teeth are either chiton longispina Saito, 2001 and Nierstraszella lineata (Nier- interlocking or actually attached to each other (between the strasz, 1905) (Fig. 2A, B). Sirenko (1992) supposed that the shaft of the major lateral and the inner small lateral teeth) to family Nierstraszellidae, which comprises single species N. transmit pressure from the cutting edge and to distribute lineata, is an intermediate link between the orders Lepido-

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Fig. 2. Central part of radulae. A, Leptochiton longispinus Saito, 2001; B, Nierstraszella lineata (Nierstrasz, 1905); C, Acanthopleura japonica (Lischke, 1873); D, Tegulaplax hululensis (Smith, 1903); E, Ferreiraella takii (Wu & Okutani, 1984). Scale bar: A: 10µm; B, D, E: 50µm; A, 100µm.

Fig. 2. Parte centrale di radule. A, Leptochiton longispinus Saito, 2001; B, Nierstraszella lineata (Nierstrasz, 1905); C, Acanthopleura japonica (Lischke, 1873); D, Tegulaplax hululensis (Smith, 1903); E, Ferreiraella takii (Wu & Okutani, 1984). Scala di riferimento: A: 10µm; B, D, E: 50µm; A, 100µm.

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Fig. 3. Radula of Acanthopleura japonica (Lischke, 1873). A, dorsal view, B, transverse section of the posterior part of the radula showing jointed petaloid processes (pp); C, close up of the jointed petaloid processes. ML, major lateral tooth; MU, major uncinus tooth; h, p, head and pore of shaft of major lateral tooth, respectively; rm, radular membrane. Scale bar: A, B: 100µm; C: 50µm.

Fig. 3. Radula di Acanthopleura japonica (Lischke, 1873). A, vista dorsale, B, sezione trasversale della parte posteriore della radula che evidenzia l’unione dei processi petaloidi(pp); C, particolare dell’unione dei processi petaloidi. ML, dente laterale maggiore; MU, dente laterale uncinato; h, p, testa e poro della parte basale del dente laterale maggiore, rispettivamente; rm, membrana radulare. Scala di riferimento: A, B: 100µm; C: 50µm.

pleurida and Chitonida. The genus Ferreiraella has a peculiar families Ischnochitonidae and Chitonidae. This may support “bud-like” process at the antero-dorsal corner (Fig. 2E, bp). the monophyly of the suborder Chitonina proposed in the It is still unclear whether or not these processes are homolo- latest system (Sirenko, 1997), if the family Callochitonidae, gous between these two suborders. Extensive study is needed which lacks this process, is removed. to fully assess this character. The central and the centro-lat- The mineralized head is conspicuous and widely variable in eral teeth do not differentiate in the Juvenichitoninae. shape, and has thus been treated as an important character Major lateral: The major lateral tooth is the dominant ele- for the recognition of species or definition of genera. Beside ment of the radula and the major scraping unit (Bullock, the “tab” used as an important character in taxonomy of the 1988a). It consists of a large, long shaft and a mineralized genus Chiton by Bullock (1988a), there are many smaller black head of dense magnetite. In many species the shaft has structures that await examination, e.g. grooves on the poste- been shown to house a large cavity which opens as a small rior surface, minute pores between the tricuspid cusps, and pore or narrow slit on the inner lateral wall (Figs. 1, 3A, p), the translucent part of the basal portion. Polymorphism of though the pore could not be found in Leptochiton assimilis the head was demonstrated by Sirenko (1974) for Tonicella (Thiele, 1909) at least. The distribution of this feature with- species and for Sypharochiton by Bullock (1988b). in the class and its function are unknown at present. A small Small laterals: The small laterals consist of two teeth on process called the “petaloid process” or “wing” (Figs. 1, 3, each side. They are usually thick, “boss-like” teeth and the pp) is present in certain groups. The function of this process inner one is firmly attached to the lateral depression in the is also unclear (Bullock, 1988a), but it may help maintain major lateral tooth. The inner small lateral of Leptochiton the “cylinder” shape of the radula and thus enable efficient tenuidontus Saito & Okutani, 1991 is elongate, like a tooth- grazing, as each pair of processes is brought together in the pick. Thermochiton undocostatus Saito & Okutani, 1991 has “cylinder” (Fig. 3B, C). Thiele (1909-1910, 1929) used the elongate inner small laterals with two spatula-shaped presence of the petaloid process as a defining character of the processes, and prow-shaped outer small laterals.

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Fig. 4. Radula of Craspedoplax. A-C, Craspedoplax variabilis (H. Adams, 1864), NSMT-Mo 72866, BL 13.2 mm. Scale bar, A, 100µm; B, C, 50µm.

Fig. 4. Radule di Craspedoplax. A-C, Craspedoplax variabilis (H. Adams, 1864), NSMT-Mo 72866, BL 13.2 mm. Scala di riferimento, A, 100µm; B, C, 50µm.

Major uncinus: The major uncinus is usually tall and of radular teeth of these species is also different from that of spoon-like in shape; however, it is reduced to a small piece of others, and a critical review of their taxonomic position is plate in Callochiton and Cryptochiton (Fig. 18). In the genera needed. Ferreiraella and Tonicella there is a rake-like blade at the apex, though the fine morphology is different. The Cryptoplacoid Radula as a Test Case Marginals: The marginals consist of three flat teeth on each side. These teeth have attracted less attention than the oth- Superfamily CRYPTOPLACOIDEA H. & A. Adams, 1858 ers, but they also have important characters. Species with a Family ACANTHOCHITONIDAE Pilsbry, 1893 large number of transverse rows of teeth, such as those of Subfamily ACANTHOCHITONINAE Pilsbry. 1893 Stenosemus, Connexochiton, Thermochiton and certain species of Leptochiton (as outlined below) have wide, short outer mar- Genus Craspedoplax Iredale & Hull, 1925 ginal teeth and small inner marginals which articulate to the major uncinus. The marginal teeth of Amicula gurjanovae Type species. Hanleya variabilis H. Adams & Angas, 1864 Yakovleva, 1952 have serrated edges (Yakovleva, 1952; Okutani & Saito, 1987). Material examined. Craspedoplax variabilis (H. Adams & Number of transverse rows: Variation in the number of Angas, 1864), NSMT-Mo 72866, 2 specimens, BL. 7.6 mm transverse rows of teeth is usually small within a genus; & 13.2 mm, Edithburg, South Australia. however, considerable differences are recognized in some genera. For example, in the genus Leptochiton, some species, Radula. The radula is symmetrical. The central tooth is such as L. assimilis (Thiele, 1909), L. surugensis Saito, 1997, moderate in size and inverse teardrop-shaped in outline. The and L. tenuidontus Saito & Okutani, 1991, have more than posterior surface is concave below the fairly large cusp and 150 rows, while others have fewer than 40. The morphology flat in the middle portion, with a keel forming towards the

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Fig. 5. Radulae of Craspedochiton. A, B, C. laqueatus (Sowerby, 1842), NSMT-Mo 71180, BL 17.3 mm; C, D, C. pyramidalis (Is. Taki, 1938), NSMT-Mo 70043, BL ca. 18 mm (AD); E, F, C. productus (Carpenter in Pilsbry, 1892), NSMT-Mo 72867, BL 41.8 mm. Scale bar: A, C, F, 50µm; B, D, 10µm; E, 100µm.

Fig. 5. Radule di Craspedochiton. A, B, C. laqueatus (Sowerby, 1842), NSMT-Mo 71180, BL 17.3 mm; C, D, C. pyramidalis (Is. Taki, 1938), NSMT-Mo 70043, BL ca. 18 mm (AD); E, F, C. productus (Carpenter in Pilsbry, 1892), NSMT-Mo 72867, BL 41.8 mm. Scala di riferimento: A, C, F, 50µm; B, D, 10µm; E, 100µm. base. The centro-lateral tooth has a thickened antero-lateral apparently wider than the others, which splay slightly out- corner bearing a narrow, indistinct cusp. The head of the wards, and the anterior surface has an irregular reticulate major lateral tooth has rather thin cusps. The central cusp is sculpture. The major uncinus tooth is narrow (Fig. 4 ).

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Fig. 6. Radulae of Notoplax. A, B, N. speciosa (H. Adams, 1861), SAM D 16073, BL ca. 29 mm, (dried material), C, N. addenda Iredale & Hull, 1925, SAM D 17944, BL 56.3 mm; D, N. sp., NSMT-Mo 70061, BL ca. 60 mm (AD). Scale bar: A-D, 100µm.

Fig. 6. Radule di Notoplax. A, B, N. speciosa (H. Adams, 1861), SAM D 16073, BL ca. 29 mm, (materiale a secco), C, N. addenda Iredale & Hull, 1925, SAM D 17944, BL 56.3 mm; D, N. sp., NSMT-Mo 70061, BL ca. 60 mm (AD). Scala di riferimento: A-D, 100µm.

Remarks. Craspedoplax Iredale & Hull, 1925 has been treat- men, BL 17.3 mm, Goto Islands, Japan. C. pyramidalis (Is. ed as a distinct genus chiefly by Australian authors (e.g. Cot- Taki, 1938), NSMT-Mo 70043, 1 specimen, BL ca. 18 mm, ton, 1964; Gowlett-Holmes, 1998), but elsewhere it has Off Izu-Oshima Island, Japan (AD). C. productus (Carpenter been synonymised with Craspedochiton (e.g. Smith, 1960; Van in Pilsbry, 1892), NSMT-Mo 72867, 1 specimen, BL 41.8 Belle, 1983; Kaas & Van Belle, 1981, Slieker, 2000). The mm, South Africa. radula of Craspedoplax variabils (H. Adams, 1864) is quite different from that of Craspedochiton species (Fig. 5), especial- Radula. The radula is small and symmetrical. The central ly in possessing a central tooth with a large cusp and narrow tooth is large and squarish in outline. The posterior surface base, and the thickened antero-dorsal corner of the centro- is mildly concave, weakly keeled and convex near the weakly lateral tooth. These differences in the radula together with bilobed base. The antero-lateral corner of the centro-lateral those in other external features such as the tegmental sculp- tooth is obtuse and smooth, thin or slightly thickened. The ture, girdle, spicules etc. confirm the validity of the genus. head of the major lateral tooth is small and has pointed cusps. The major uncinus tooth has a narrow blade (Fig. 5). Genus Craspedochiton Shuttleworth, 1853 Remarks. The radula of Spongiochiton productus Carpenter in Type species. Chiton laqueatus Sowerby, 1842 Pilsbry, 1892, the type species of Spongiochiton is essentially Material examined. Craspedochiton laqueatus (Sowerby, the same as that of Craspedochiton species. The other charac- 1842), NSMT-Mo 70040, 1 specimen, BL ca. 24 mm, Off ters of Craspedochiton, such as the peculiar tegmental sculp- Amakusa Islands, Japan (AD); NSMT-Mo 71180, 1 speci- ture, wide expansion of the anterior girdle, and the enlarged,

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Fig. 7. Radulae of Cryptoconchus. A, B, C. porosus (Blainville MS, Burrow, 1815), NSMT-Mo 72868, 1 specimen, BL. 43.5 mm, (AD); C, D, “Cryptoconchus” burrowi Nierstrasz, 1905, NSMT-Mo 70111, BL ca. 18 mm (AD); E, F, “Cryptoconchus” floridanus (Dall, 1889), FSBC I 32081, BL 13.6 mm. Scale bar: A, D, 100µm; B, 500µm; C, F, 50µm; E, 10µm.

Fig. 7. Radule di Cryptoconchus. A, B, C. porosus (Blainville MS, Burrow, 1815), NSMT-Mo 72868, 1 esemplare, BL. 43.5 mm, (AD); C, D, “Cryptoconchus” burrowi Nierstrasz, 1905, NSMT-Mo 70111, BL ca. 18 mm (AD); E, F, “Cryptoconchus” floridanus (Dall, 1889), FSBC I 32081, BL 13.6 mm. Scala di riferimento: A, D, 100µm; B, 500µm; C, F, 50µm; E, 10µm. leaf-like scales of the hyponotum are also present in S. pro- Genus Notoplax H. Adams, 1861 ductus. Spongiochiton is thus regarded as a synonym of Craspe- dochiton. Type species. Cryptoplax (Notoplax) speciosa H. Adams, 1861

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Fig. 8. Radulae of Leptoplax. A, B, Leptoplax coarctata (Sowerby, 1841), NSMT-Mo 70109, BL 15.2 mm (AD); C, D, L. doederleini (Thiele, 1909), NSMT-Mo 70088, BL ca. 25 mm, Boso Peninsula, Japan (AD); E, F, L. curvisetosa (Leloup, 1960), NSMT-Mo 72869, BL. 9.0 mm, Aqaba, Jor- dan. Scale bar: A, E, 10µm; B-D, F, 50µm.

Fig. 8. Radule di Leptoplax. A, B, Leptoplax coarctata (Sowerby, 1841), NSMT-Mo 70109, BL 15.2 mm (AD); C, D, L. doederleini (Thiele, 1909), NSMT-Mo 70088, BL ca. 25 mm, Boso Peninsula, Japan (AD); E, F, L. curvisetosa (Leloup, 1960), NSMT-Mo 72869, BL. 9.0 mm, Aqaba, Jor- dan. Scala di riferimento: A, E, 10µm; B-D, F, 50µm.

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Material examined. Notoplax speciosa (H. Adams, 1861), South Australia. N. sp., NSMT-Mo 70061, 1 specimen, BL SAM D 16073, 1 specimen; BL ca. 29 mm, (dried material), ca. 60 mm, Amakusa Islands, Japan (AD). Clenery, South Australia. N. addenda Iredale & Hull, 1925, SAM D 17944, 1 specimen; BL 56.3 mm, Eyre Peninsula, Radula. The radula is asymmetrical; the teeth on the left

Fig. 9. Radulae of Bassethullia and Pseudotonicia. A, C, E, Bassethullia matthewsi (Bednall & Pilsbry in Pilsbry, 1894), NSMT-Mo 72870, BL. ca. 25 mm; B, D, F, Pseudotonicia cuneata (Suter, 1908), SAM D 18604, 1 specimen, BL 54.5 mm. Scale bar: A, B, E, F, 100µm; C, D, 50µm.

Fig. 9. Radule di Bassethullia e Pseudotonicia. A, C, E, Bassethullia matthewsi (Bednall & Pilsbry in Pilsbry, 1894), NSMT-Mo 72870, BL. ca. 25 mm; B, D, F, Pseudo- tonicia cuneata (Suter, 1908), SAM D 18604, 1 esemplare, BL 54.5 mm. Scala di riferimento: A, B, E, F, 100µm; C, D, 50µm.

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Fig. 10. Radulae of Acanthochitona fascicularis species-group. A, A. fascicularis (Linné, 1767), NSMT-Mo72871, BL 29.4 mm; B, A. achates (Gould, 1859), NSMT- Mo72879, BL 25.5 mm, (AD); C, A. exquisita (Pilsbry, 1893), NSMT-Mo 72872, BL 24.6 mm; D, A. defilippii (Tapparone-Canefri, 1874), NSMT-Mo 72882, BL ca. 43 mm, (AD). Scale bar: A-D, 100µm.

Fig. 10. Radule delle specie appartenenti al gruppo Acanthochitona fascicularis. A, A. fascicularis (Linné, 1767), NSMT-Mo72871, BL 29.4 mm; B, A. achates (Gould, 1859), NSMT-Mo72879, BL 25.5 mm, (AD); C, A. exquisita (Pilsbry, 1893), NSMT-Mo 72872, BL 24.6 mm; D, A. defilippii (Tapparone-Canefri, 1874), NSMT-Mo 72882, BL ca. 43 mm, (AD). Scala di riferimento: A-D, 100µm. side are higher or staggered behind those on the right side. la as that of Notoplax described above, e.g. “Notoplax” conica The central tooth is asymmetrical, large, squarish, mildly Is. & Iw. Taki, 1929 and “N” hilgendorfi Thiele, 1909 but in concave in the distal half and bilobed at the base. The cen- these cases the other morphological characters do not match tro-lateral tooth has a thin, weakly notched antero-dorsal well. corner. The head of the major lateral tooth is large, with a long median denticle and a dorsal groove. There are orange, Genus Cryptoconchus Blainville MS, Burrow, 1815 translucent, triangular portions on both basal sides of the head. The major uncinus tooth is very slender (Fig. 6). Type species. Chiton porosus (Blainville MS) Burrow, 1815 Remarks. This genus has hitherto been considered endemic to Australian and New Zealand waters (Gowlett-Holmes, Material examined. Cryptoconchus porosus (Blainville MS, 1991). The characters of the valves, girdle, and the radula of Burrow, 1815), NSMT-Mo 72868, 1 specimen, BL. 43.5 the Japanese species examined in this study agree well with mm, Katai Bay, New Zealand (AD). “Cryptoconchus” flori- the redefinition of Notoplax by Gowlett-Holmes (1991). danus (Dall, 1889), FSBC I 32081, 1 specimen, BL 13.6 mm. However, the Japanese species has a tubular stomach that Key Vaca, Florida Keys. “Cryptoconchus” burrowi Nierstrasz, lacks a ventral pouch. The Australian species Notoplax adden- 1905, NSMT-Mo 70111, BL ca. 18 mm, Amami-Oshima da Iredale & Hull, 1925 has a large pouch, but no pouch was Id., Japan (AD). observed in a dried specimen of N. speciosa (H. Adams, 1861). Radula. The radula of Cryptoconchus porosus (Dall, 1889) (Fig. There are several species which have basically the same radu- 7a, b) is essentially the same as that of Notoplax (Fig. 6).

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Fig. 11. Radulae of Acanthochitona intermedia species-group. A, B, A. intermedia (Nierstrasz, 1905), NSMT-Mo 72878, BL ca. 23 mm, (AD), C, D, A. penicilata (Deshayes, 1863), NSMT-Mo 72873, BL 11. 8 mm (dried specimen), E, F, A. mastalleri Strack,1989, NSMT-Mo 72874, BL 6.6 mm (dried specimen). Scale bar: A, C, 100µm; B, E, 50µm; D, F, 10µm.

Fig. 11. Radule delle specie appartenenti al gruppo Acanthochitona intermedia. A, B, A. intermedia (Nierstrasz, 1905), NSMT-Mo 72878, BL ca. 23 mm, (AD), C, D, A. penicilata (Deshayes, 1863), NSMT-Mo 72873, BL 11. 8 mm (esemplare a secco), E, F, A. mastalleri Strack,1989, NSMT-Mo 72874, BL 6.6 mm (esemplare a secco). Scala di riferimento: A, C, 100µm; B, E, 50µm; D, F, 10µm.

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Remarks. In addition to the radula, similarities in valve morphology, such as the outline of the valves, suggest a close Genus Leptoplax Carpenter MS, Dall, 1882 relationship between Cryptoconchus and Notoplax. The other two species, which have been placed in Crypto- Type species. Chiton coarctatus Sowerby, 1841 conchus, namely, “C.” floridanus (Dall, 1889) and “C.” burrowi Nierstrasz, 1905 have quite different radulae (Fig. 7c-f). The Material examined. Leptoplax coarctata (Sowerby, 1841), radula of “C.” floridanus is symmetrical. The central tooth is NSMT-Mo 70109, 2 specimens, BL ca. 10 mm & 15.2 mm, small, with a prominent keel. The centro-lateral has a thick- Iriomote Island, Japan (AD). L. doederleini (Thiele, 1909), ened, nodulous antero-dorsal corner. The head of the major NSMT-Mo 70088, 1 specimen, BL ca. 25 mm, Boso Penin- lateral has rather thin cusps, which have a minute pore sula, Japan (AD); NSMT-Mo 70089, 1 specimen, BL ca. 15 between them. The major uncinus is moderate in width. mm, Izu Peninsula, Japan (AD), L. curvisetosa (Leloup, 1960), These radular characters and certain aspects of valve mor- NSMT-Mo 72869, 1 specimen, BL. 9.0 mm, Aqaba, Jordan phology, especially the two slits in the tail valve, suggest a Radula. The radula is symmetrical. The central tooth is closer relationship between “C.” floridanus and Acanthochitona spatula-shaped, pointed and keeled in the basal portion. than between the former and Cryptoconchus. The radula of There is no cusp at the tip. The centro-lateral tooth has a “C.” burrowi is essentially the same as that of Leptoplax (Fig. slightly thickened antero-dorsal corner. The head of the 8). The characters of the valves and the girdle also suggest a major lateral tooth is large, with blunt cusps having a flat close relationship with Leptoplax. These two species should anterior surface. The major uncinus is narrow to moderate in clearly be removed from Cryptoconchus, but as they are also width (Fig. 8). different from related genera as outlined above, further study is needed to determine their correct generic assignment. Remarks. The genus Leptoplax was treated as a synonym of

Fig. 12. Radulae of Acanthochitona dissimilis species group. A, B, A. sueurii (Blainville, 1825), NSMT-Mo 72877, BL 16.5 mm, (AD); C, A. sp., NSMT-Mo 72875, BL ca. 7 mm, Chichijima Island, Japan (AD); D A. dissimilis Is. & Iw. Taki, 1931, NSMT-Mo 73023, BL 13.7 mm. Scale bar: A-C, 100µm; D, 50µm.

Fig. 12. Radule delle specie appartenenti al gruppo Acanthochitona dissimilis. A, B, A. sueurii (Blainville, 1825), NSMT-Mo 72877, BL 16.5 mm, (AD); C, A. sp., NSMT-Mo 72875, BL ca. 7 mm, Chichijima Island, Japan (AD); D A. dissimilis Is. & Iw. Taki, 1931, NSMT-Mo 73023, BL 13.7 mm. Scala di riferimento: A-C, 100µm; D, 50µm.

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Fig. 13. Radula of Choneplax. A-D, C. lata (Guilding, 1829), FSBC I 32548, BL 25.2 mm. Scale bar: A, 100µm; B, C, 10µm; D, 50µm.

Fig. 13. Radula di Choneplax. A-D, C. lata (Guilding, 1829), FSBC I 32548, BL 25.2 mm. Scala di riferimento: A, 100µm; B, C, 10µm; D, 50µm.

Notoplax which had been considered a heterogeneous genus bry in Pilsbry, 1894), NSMT-Mo 72870, 1 specimen, BL. ca. characterised by multiple slits in the tail valve. Since 25 mm, Moana Reef, South Australia. Gowlett-Holmes (1991) redefined the genus Notoplax, those heterogeneous genera have once more been divided. The Radula. The radula is symmetrical. The central tooth is nar- genus Leptoplax has previously also been regarded as a dis- row, spatula-shaped and keeled near the base. The apical tinct genus (Gowlett-Holmes, 1998; Saito, 2001), although edge has no blade. The centro-lateral tooth has a thickened sufficient definition of the genus has not yet been provided. and somewhat nodulous antero-dorsal corner. The head of The peculiar radular morphology of Leptoplax supports sepa- the major lateral tooth has rather thin cusps. The central ration at generic level. cusp is apparently wider than the others, which splay slightly outwards. The major uncinus tooth is moderate in width Genus Bassethullia Pilsbry, 1928 (Fig. 9A, C, E).

Type species. Acanthochites matthewsi Bednall & Pilsbry in Remarks. The radulae of the other two species of Bassethul- Pilsbry, 1894 lia, B. glypta (Sykes, 1896) and B. porcina (Ashby, 1919), which were illustrated by Gowlett-Holmes (1990), have Material examined. Bassethullia matthewsi (Bednall & Pils- essentially the same morphology as that of B. matthewsi. The

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Fig. 14. Radula of Cryptochiton. A, B, C. stelleri (Middendorff, 1847): NSMT-Mo 72887, BL 125 mm (AD). Scale bar: A, B, 100µm.

Fig. 14. Radula di Cryptochiton. A, B, C. stelleri (Middendorff, 1847): NSMT-Mo 72887, BL 125 mm (AD). Scala di riferimento: A, B, 100µm.

Fig. 15. Radula of Hemiarthrum. H. setulosum Dall, 1876, NSMT-Mo 72883, BL ca. 10 mm. Scale bar: A, C, 50µm; B, 10µm.

Fig. 15. Radula di Hemiarthrum. H. setulosum Dall, 1876, NSMT-Mo 72883, BL ca. 10 mm. Scala di riferimento: A, C, 50µm; B, 10µm.

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morphology of the central and the centro-lateral teeth of Bassethullia is somewhat similar to that of Leptoplax, while Genus Pseudotonicia Ashby, 1928 the head of the major lateral tooth, with its rather thin cusps and wider central cusp, is similar to those of Craspedoplax Type species. Tonicia cuneata Suter, 1908 and Pseudotonicia.

Fig. 16. Radulae of Cryptoplax. A, B, C. larvaeformis (Blainville MS, Burrow, 1815), NSMT-Mo 72885, BL ca. 40 mm (AD); C, C. japonica Pilsbry, 1901, NSMT-Mo 72884, BL ca. 100 mm (AD); D, C. striata (Lamarck, 1819), NSMT-Mo 72887, BL ca. 50 mm, (AD); E, F, C. elioti Pilsbry, 1901, NSMT-Mo 72886, BL 76.0 mm (AD). Scale bar: A, B, E, F, 100µm; C, D, 50µm.

Fig. 16. Radule di Cryptoplax. A, B, C. larvaeformis (Blainville MS, Burrow, 1815), NSMT-Mo 72885, BL ca. 40 mm (AD); C, C. japonica Pilsbry, 1901, NSMT-Mo 72884, BL ca. 100 mm (AD); D, C. striata (Lamarck, 1819), NSMT-Mo 72887, BL ca. 50 mm, (AD); E, F, C. elioti Pilsbry, 1901, NSMT-Mo 72886, BL 76.0 mm (AD). Scala di riferimento: A, B, E, F, 100µm; C, D, 50µm.

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than to common ancestry. The general appearance of the Material examined. Pseudotonicia cuneata (Suter, 1908), radula is different between the two taxa but the similarity of SAM D 18604, 1 specimen, BL 54.5 mm, Tauranga Har- the major lateral tooth may suggest common ancestry. bour, New Zealand. Genus Acanthochitona Gray, 1921 Radula. The radula is symmetrical. The central tooth is fairly large, roughly oblong in outline, convex, and faintly Type species. Chiton fascicularis Linné, 1767 keeled near the base. There is a weak blade at the apex. The centro-lateral tooth is angulate with a faint cusp at the Material examined. Acanthochitona fascicularis (Linné, antero-dorsal corner. The head of the major lateral tooth has 1767), NSMT-Mo72871, 1 specimen, BL 29.4 mm, Bre- rather thin cusps. The central cusp is apparently wider than tagne, France. A. achates (Gould, 1859), NSMT-Mo72879, 1 the others, which splay slightly outwards. The major unci- specimen, BL 25.5 mm, Nagasaki, Japan (AD); NSMT-Mo nus is narrow (Fig. 9B, D, F). 72880, 1 specimen, BL 25.5 mm, Muroran, Japan (AD); NSMT-Mo 72881, 1 specimen, BL 41.5 mm, Izu-Oshima Remarks. Gowlett-Holmes (1991) stated that P. cuneata Island, Japan. A. exquisita (Pilsbry, 1893), NSMT-Mo (Suter, 1908) resembles Bassethullia in appearance and habi- 72872, 1 specimen, BL 24.6 mm, Baja California, Mexico. tat; however, the similarities between them may be attribut- A. defilippii (Tapparone-Canefri, 1874), NSMT-Mo 72882, 1 able to convergent evolution towards a similar habitat rather specimen, BL ca 43 mm, Aoshima, Japan (AD). A. intermedia

Fig. 17. A,C, Radula of Lepidozona coreanica (Reeve, 1847) NSMT-Mo 72891, BL 42.0 mm. B,D, Lorica cimolia (Reeve, 1847) NSMT-Mo 72892, BL 46.5 mm. ap, accessory process; pp, petaloid process. Scale bar: A-D, 100µm.

Fig. 17. A,C, Radula di Lepidozona coreanica (Reeve, 1847) NSMT-Mo 72891, BL 42.0 mm. B,D, Lorica cimolia (Reeve, 1847) NSMT-Mo 72892, BL 46.5 mm. ap, processo accessorio; pp, processo petaloide. Scala di riferimento: A-D, 100µm.

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Fig. 18. A, Radula of Callochiton foveolatus (Is. Taki, 1938). NSMT-Mo 72890, BL 18.5 mm. B, Radula of Cryptochiton stelleri (Middendorff, 1847): NSMT-Mo 72887, BL 125 mm (AD). Scale bar: A, B, 50µm.

Fig. 18. A, Radula di Callochiton foveolatus (Is. Taki, 1938). NSMT-Mo 72890, BL 18.5 mm. B, Radula di Cryptochiton stelleri (Middendorff, 1847): NSMT-Mo 72887, BL 125 mm (AD). Scala di riferimento: A, B, 50µm. (Nierstrasz, 1905), NSMT-Mo 72878, 1 specimen, BL ca. 23 Radula. The radula is symmetrical. The central tooth is mm, Amami-Oshima Island, Japan (AD), A. penicilata small, narrow and spatula-shape in outline; the posterior (Deshayes, 1863), NSMT-Mo 72873, 1 specimen, BL 11. 8 surface is mildly concave in the distal half and sharply keeled mm (dried specimen), Aqaba, Jordan, A. mastalleri in the basal portion. The anterior process is short and adher- Strack,1989, NSMT-Mo 72874, 1 specimen, BL 6.6 mm ent at the base. The centro-lateral tooth has a thick and (dried specimen), Pharaon Island, Egypt. A. dissimilis Is. & knobbed antero-dorsal corner. The head of the major lateral Iw. Taki, 1931, NSMT-Mo 72876, 1 specimen, BL ca. 13 tooth is large with a flat anterior surface. Each of the three mm, Boso Peninsula, Japan (AD); NSMT-Mo 73023, 1 spec- denticles has an obtuse tip. The major uncinus tooth has a imen, BL 13.7 mm, Boso Peninsula, Japan. A. sp., NSMT- blade of moderate width (Fig. 11). Mo 72875, 1 specimen, BL ca. 7 mm, Chichijima Island, Japan (AD). A. sueurii (Blainville, 1825), NSMT-Mo 72877, 3) dissimilis-group. This group consists of A. dissimilis, A. 1 specimen, BL 16.5 mm, Edithburg, South Australia (AD). sueurii, and A. sp. They are characterised by very fine “asbestoid” sutural tufts and fine granular spicules on the At least three species groups featuring different types of perinotum. radula are recognized within this genus. 1) fascicularis-group. This group consists of A. fascicularis, Radula. The radula is symmetrical except for the central A. exquisita, A. defilippii, and A. achates. They are character- tooth of A. dissimilis, which is slightly asymmetrical. The ized by a bimorphic perinotum, which gives a heavily spicu- central tooth is small, narrow in outline, thick, rather deeply lous appearance. concave on the distal half and keeled at the basal portion. The anterior process is long and entirely adherent. The cen- Radula. The radula is symmetrical. The central tooth is tro-lateral tooth has a thick and knobbed antero-dorsal cor- small and squarish in outline; the posterior surface is mildly ner. The head of the major lateral tooth is large and the three concave in the distal half, and somewhat keeled and dilated denticles are rather narrow and of nearly the same length. in the basal half. The anterior process is short and adherent The major uncinus tooth has a rather narrow blade (Fig. 12). in the basal half. The centro-lateral tooth has a nodulous antero-dorsal corner. The head of the major lateral tooth is Remarks. As shown above, the radula of Acanthochitona is large and has a rounded anterior surface; the median denticle variable among species groups; however it is consistently is apparently larger than the others. The major uncinus tooth characterised by the nodulous antero-lateral corner of the has a fairly wide blade (Fig. 10). centro-lateral tooth. The genus Acanthochitona contains many species, the morphology of which is little known. The taxo- 2) intermedia-group. This group consists of A. intermedia, nomic status of each species-group must await more exten- A. penicilata, and A. mastalleri. They are characterized by sive study of this genus. thin, whitish valves and a monomorphic perinotum consist- ing of slender spicules. Genus Choneplax Dall, 1882

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Type species. Chitonellus latus Guilding, 1829 the head valve. Watters (1991) recommended reconsidera- Material examined. Choneplax lata (Guilding, 1829), FSBC tion of its taxonomic position. The radula morphology of I 32548, 1 specimen, BL 25.2 mm, Grand Bahama Island; Cryptochiton stelleri (Middendorff, 1847) is quite different USNM 886327, 1 specimen, BL ca. 25 mm, Carrie Bow Cay, from that of other members of the Cryptoplacoidea and this Belize. also supports the need for reconsideration of its systematic status. Radula. The radula is symmetrical. The central tooth is oblong in outline, weakly keeled near the base; there is a Family HEMIARTHRIDAE Sirenko, 1997 fairly wide cusp at the apex. The centro-lateral tooth has a nodular antero-dorsal corner. The head of the major lateral Genus Hemiarthrum Dall, 1876 tooth has short cusps of almost equal size and a flat anterior surface. The major uncinus tooth is moderate in width (Fig. Type species. Hemiarthrum setulosum Dall, 1876 13). Material examined. Hemiarthrum setulosum Dall, 1876, Remarks. The valve morphology of Choneplax has certain NSMT-Mo 72883, 1 specimen, BL ca. 10 mm, King George characters in common with both Acanthochitona and Crypto- Island, Antarctica. plax, and it has thus been placed variously in the Acantho- chitonidae/inae (Pilsbry, 1893; Thiele, 1909; 1929; Kaas, Radula. The radula is symmetrical. The central tooth is fair- 1972; Kaas & Van Belle, 1980; 1998) and in the Crypto- ly large, spatula-shaped, pointed and keeled in the basal por- placidae/inae (Bergenhayn, 1955; Van Belle, 1983; Lyons, tion. The apical edge forms a wide cusp with a central notch. 1988; Sirenko, 1997). Thiele (1909) pointed out that the The centro-lateral tooth has a thin, angulate antero-dorsal radula of Choneplax lata is similar to that of Cryptoplax corner, which curves inward, forming a small cusp. The head striata. The present study reveals that the radular features are of the major lateral tooth has a wide middle cusp and two also intermediate in nature; the grooved antero-dorsal corner smaller cusps, separated by faint grooves that reach the basal of the centro-lateral tooth is similar to that of Cryptoplax, portion. The major uncinus is narrow (Fig. 15). while in central tooth characters Choneplax more closely resembles Acanthochitona than Cryptoplax. Remarks. Sirenko (1997) separated this genus from Han- Subfamily CRYPTOCHITONINAE Pilsbry, 1893 leyidae and placed it in the new family Hemiarthridae, which he created in the superfamily Cryptoplacoidea based Genus Cryptochiton Middendorff, 1847 on differences in gill arrangement, articulamentum, innerva- tion to the aesthetes and sutural tufts on the perinotum. The Type species. Chiton stelleri Middendorff, 1847 radular characters do not contradict his assignment; on the contrary, no radular character has so far been identified that Material examined. Cryptochiton stelleri (Middendorff, is common only to the Cryptoplacoidea. 1847): NSMT-Mo 72887, 1 specimen, BL 125 mm, Shire- toko Peninsula, Japan (AD); NSMT-Mo 72888, 1 specimen, Family CRYPTOPLACIDAE H. & A. Adams, 1858 BL ca. 100 mm, Akkeshi, Japan (AD); NSMT-Mo 72889, 1 specimen, BL 23 mm, Noshappu, Japan (AD). Genus Cryptoplax Blainville, 1818

Radula. The radula shows slight asymmetry, and the rows are skewed. The central tooth is small; the main plate is Type species. Chiton larvaeformis Blainville MS, Burrow, roughly elongate pentagonal in outline, obtuse at the dorsal 1815 edge, and bilobed ventrally with double keels along the medial line in the ventral half. The centro-lateral tooth is Material Examined. Cryptoplax larvaeformis (Blainville MS, expanded laterally at the antero-lateral edge. The head of the Burrow, 1815), NSMT-Mo 72885, 1 specimen, BL ca. 40 major lateral tooth is large but rather thin, and only slightly mm, Iriomote Island, Japan (AD), C. japonica Pilsbry, 1901, expanded posteriorly at the juncture with the shaft. The NSMT-Mo 72884, 1 specimen, BL ca 100 mm, Boso Penin- median denticle of the head is apparently larger than the sula, Japan (AD). C. striata (Lamarck, 1819), NSMT-Mo others. The shaft is long and dilated ventrally, and widened 72887, 1 specimen, BL ca. 50 mm, Point Souttar, South and curved dorsally in the anterior portion. The major unci- Australia (AD). C. elioti Pilsbry, 1901, NSMT-Mo 72886, 1 nus tooth is reduced to a basal plate and a minute isolated specimen, BL 76.0 mm, Tokashiki Island, Japan (AD). fragment (Fig. 14). Radula. The radula is symmetrical. The central tooth is Remarks. This monotypic genus has been placed in the fam- small, thick, and oblong in outline. The posterior surface is ily Acanthochitonidae, based on the reduced tegmentum, the clearly concave in the upper half and keeled near the base. presence of spinous tufts, and the small number of slits in The anterior process is short and adherent at the base. The

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centro-lateral tooth has a nodulous antero-dorsal corner with Bullock, 1988), the exact size, number, and localities of a groove on the inner surface. The head of the major lateral specimens examined in every study should be recorded in the tooth has short, almost equal-sized, obtuse cusps, and a flat resulting articles. It is interesting that the tricuspid head of anterior surface. The major uncinus tooth is moderate in the major lateral tooth appears in the early life stage in width (Fig. 16). examples of Lepidopleurida and Chitonida. The initial stages of radular development in several chitons imply an Remarks. The central tooth varies among species, but it is ancestral radular state in the Mollusca (Sirenko & Minichev, consistently characterised by its small size and keeled, squar- 1975; Eernisse & Kerth, 1988). Further research into onto- ish base. The radula of Cryptoplax resembles that of Acantho- genetic variation may provide clues into the phylogeny of chitona in the nodulous antero-dorsal corner of the centro-lat- chitons. eral tooth, but differs by having a groove on the inner wall of The present study suggests that radular characters may be the antero-dorsal corner. most effective in evaluating the phylogenetic relationships within a genus and/or a family, as demonstrated here using CONCLUSIVE REMARKS the example of the superfamily Cryptoplacoidea. Compar- Thiele (1893) established a large number of Polyplacophoran isons of radular characters suggest that a significant reduc- genera based on study of the radula; however, those parts of tion in the tegmentum occurred in parallel within the Cryp- his work based solely on radular characters have seldom been toplacoidea, namely in the lineages of Notoplax-Cryptoconchus, accepted by subsequent authors. Bullock (1988) remarked of Leptoplax, Acanthochitona and Cryptochiton. Radular characters the characteristic ischnochitonid radula of the chitonid Rad- might also be useful at family or higher taxonomic levels. sia: “It should be noted that if one were classify the Polypla- Unfortunately, there are still few established or candidate cophora solely on the basis of the radula, Radsia would be characters; for example, I have not yet found any radular placed in the Ischnochitonidae. In fact, Thiele (1893, 1909), character common only to the Cryptoplacoidea. This means who emphasized the radula as a phylogenetic tool, placed R. that assignment of Hemiarthrum to the superfamily Crypto- nigrovirescens Blainville, 1825 in the genus Ischnochiton”. Bul- placoidea (Sirenko, 1997) cannot at present be based on lock (ibid) also identified similarities in valve characters radular characters, however there are some useful established between R. nigrovirescens and the ischnochitonid Ischnoradsia and candidate characters at higher taxonomic levels. For australis (Sowerby, 1840). The exact systematic position of example, the petaloid process of the major lateral tooth may Radsia is unclear, but his comparison of radular characters be an “innovative” or a character shared within the suborder provided an important clue to their phylogenetic relation- Chitonina, and the accessory process of the centro-lateral ship. A similar example is that of the ischnochitonid Lepido- tooth is possibly a new character useful at higher taxonomic zona and the loricid Lorica (Fig. 17) and an extreme example levels. I would like to propose that the radulae of Lepido- is the resemblance between the radulae of Callochiton and pleurida be extensively studied to establish useful characters Cryptochiton (Fig. 18). Morphological characters other than for work at higher taxonomic levels because, although their radular are totally different in these two genera and no one at fine morphology is poorly known, even the limited numbers present supports the notion of a close relationship; future of species examined in detail so far exhibit wide morphologi- study may or may not establish the truth. We should never- cal variation and similar morphology to species in the Chi- theless explore phylogeny by a holistic approach, and radula tonida. Any and all efforts to reveal the fine morphology of should therefore be treated as one character among many and the radulae and explore new characters are to be greatly explored to find new characters. encouraged. The crucial problem in using radular characters in systematics is the lack of adequate data concerning their fine mor- ACKNOWLEDGMENTS phology. Many radular characters have been described and I would like to thank Dr. B. Dell’Angelo, the Società Ital- illustrated in the literature, but most were based on optical iana di Malacologia, and the Istituzione Culturale Federico II microscope observation, sometimes, moreover, confined to a of Menfi for granting me the opportunity to participate in few sections such as the three central teeth. To assess phylo- the 4th International Workshop of Malacology “Systematics, genetic relationships, further morphological comparisons Phylogenesis and Biology of Polyplacophora”, and to con- using SEM and light microscopy are essential. The latter is tribute to this volume of the proceedings. still necessary for certain characters, for example the translu- I must also thank the following people and institutions for cent part, the tab on the head of the major lateral and the generously loaning or donating valuable specimens: Messrs. accessory process of the centro-lateral tooth (which is easily B. Anseeuw and Y. Terryn, the late Mr. C. Ebreo, Ms. S. L. detached during preparation for SEM examination). Accu- Farrington and Dr. W. Lyons (FSBC), Ms. K. L. Gowlett- mulation of information on fine radular morphology will Holmes, Dr. M. G. Harasewych (USNM), Dr. T. Kikuchi, enable us to make exact comparisons and will lead us to the Dr. S. Nishihama, Dr. H. Numanami, Dr. T. Sasaki, Mr. H. discovery of new characters. Strack, the late Mr. T. Tateshi and Dr. W. Zeidler (SAM),. Because ontogenetic variation and polymorphism in radula Finally, I am grateful to Dr. T. Okutani, Mr. P. Callomon have been established (Sirenko, 1974, 1992; O’Neill, 1984; and Dr. L. Cao for their critical reading of the manuscript.

> 102 < Phylogenetic significance of the radula in chitons, with special reference to the Cryptoplacoidea (Mollusca: Polyplacophora)

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